1. Field of the Invention
This invention relates to the joining of pipes wherein a sealing gasket is used to make the pipes fluid (gas or liquid) tight.
2. Description of the Prior Art
The use of a gasket in a groove is well known in joining pipe. However, the effectiveness of any gasket largely depends upon the interaction of the gasket with respect to the two interconnected pipes. "Interconnected" is herein used to mean the arrangement wherein a portion of one pipe is contained within a portion of a second pipe, respectively an inner and outer pipe. The solution to the problem of maintaining the gasket in a fixed position between two interconnected pipes has been approached by having a groove either in the internal wall of the outer pipe or the outer wall of the inner pipe. The geometry of this groove has been varied in attempts to overcome the problem from the tendency of the relative movement of the pipe walls inner or outer pipe to displace the gasket out of said groove. The term used to describe this displacement problem is "fishmouthing".
One proposal of the prior art was to provide a rectangular groove having steep sides. This was alleged to overcome the problem of fishmouthing much better than a curved or bell-shaped groove. However, rectangular grooves create a problem because in forming the vertical walls and sharp-angled corners of said grooves there is a thinning of the pipe wall and new stresses are locked in the grooves, thus weakening the pipe and making it susceptible to damage.
Another proposal was to use a gasket whose durometer (hardness) is not homogenous having a harder portion alleged to hold the gasket in position in one pipe and a softer portion positioned to form the seal with a second pipe. One such gasket was designed to be positioned in a generally trapezoidal groove.
In summary, the solutions proposed by the prior art involve either the geometry of a single groove or the physical properties of the gasket; as for example, differential hardness.